guard
楅 centers on a wooden guard or barrier, likely a physical protective device made of wood.
楅 combines 木 (tree/wood) with 畐, which likely contributes the sound. The exact historical development is uncertain, but the character likely referred to a wooden object used for guarding or blocking.
A wooden 木 barrier 畐 stands guard, like a wooden fence protecting a field.
For ヒュク, imagine a wooden guard shouting 'Hugh! Cue!' as he blocks the way: Hugh-cue -> ヒュク.